Technical Field
Embodiments described herein relate generally to a hydrogen production technique for producing hydrogen by using a high temperature electrolysis.
Description of the Related Art
Realization of a hydrogen energy society using hydrogen as an energy medium is attracting attention. A high temperature electrolysis method is widely known as one of techniques for producing hydrogen. The high temperature electrolysis method is a method for generating hydrogen and oxygen through an electrolysis of high temperature steam.
This method has an advantage that, because steam is electrolyzed in a high temperature environment, an amount of electricity necessary for the electrolysis can be reduced compared with an electrolysis of water. Owing to this feature, the same amount of hydrogen production can be obtained with electric power that is smaller by about 30% than that in the electrolysis of water at a room temperature, and hence the hydrogen production can be performed with high energy efficiency.
Because a raw material is water, if electricity based on renewable energy without generation of carbon dioxide and a heat source without generation of carbon dioxide are used, the hydrogen production can be achieved without no emission of carbon dioxide.
The following three methods are known as a hydrogen storage method for temporarily storing produced hydrogen: (1) hydrogen is compressed to a high-pressure hydrogen gas; (2) hydrogen is made into liquid hydrogen; and (3) hydrogen is occluded by a hydrogen storage material. Of these methods, the method of compressing the produced hydrogen into high pressure hydrogen gas enables easy storage and transport of hydrogen, and thus is widely prevalent.
Up to now, a technique for improving heat efficiency in an entire system by combining a hydrogen production technique and a hydrogen storage technique with each other has been studied.
For example, Patent Document 1 (Japanese Patent Laid-Open No. 2004-197705) discloses a technique including: a hydrogen production system that produces hydrogen; a hydrogen compression system that compresses the produced hydrogen up to a predetermined pressure; a hydrogen supply system that supplies the compressed high pressure hydrogen to a hydrogen consumption engine; and a combustion-turbine power generation system that covers the entirety or a part of electric power consumed by the supply system of the high pressure hydrogen. In this technique, the entirety or a part of an amount of heat required for a dehydrogenation reaction is covered using high temperature gas emitted by the combustion-turbine power generation system as a heat source.
Patent Document 2 (Japanese Patent Laid-Open No. 2009-221045) discloses a power generation-hydrogen production system including: a power generation-hydrogen pump combination member that produces hydrogen gas or generates electric power using reformed gas as a raw material; a hydrogen gas supply system that sequentially supplies high pressure hydrogen gas obtained by compressing the produced hydrogen, to a hydrogen tank of a fuel cell vehicle; a hot-water supply system that supplies hot water utilizing waste heat generated along with the power generation by the power generation-hydrogen pump combination member; and an inverter capable of converting the electric power generated by the power generation-hydrogen pump combination member and selling the electric power to a commercial power supply or outputting an electricity load to a house.
In the hydrogen storage method of compressing the produced hydrogen into high pressure hydrogen gas, heat is generated when the hydrogen is compressed. In conventional techniques, cooling is performed when hydrogen is compressed, and thermal energy generated when the hydrogen is compressed is not effectively utilized to improve hydrogen production efficiency (which is obtained by dividing an amount of hydrogen production or an amount of combustion heat of the produced hydrogen by an amount of heat input).